1. Field of the Invention
The invention relates to acrylate or methacrylate ester modified organopolysiloxane mixtures, their preparation and the use of these mixtures as abhesive coating compositions. The expression "(meth)acrylate esters" is intended to include acrylate, as well as the methacrylate esters.
2. Description of the Prior Art
German Pat. No. 27 47 233 discloses a process for the synthesis of acrylate or methacrylate ester modifified organopolysiloxanes by reacting (meth)acrylate esters having --COH groups with organopolysiloxanes having SiX groups (X=alkoxy, hydroxyl or chloro), optionally in the presence of catalysts. The organopolysiloxanes used have the formula ##STR1## wherein R.sup.1 is an alkyl group with 1 to 4 carbon atoms and/or a phenyl group,
X is a chloro or OR.sup.2 group, PA1 R.sup.2 is an alkyl group with 1 to 4 carbon atoms and/or hydrogen, PA1 a has a value of 1.0 to 2.0, PA1 b has a value of 0.02 to 1.6, and PA1 a+b is not greater than 2.66, and wherein the siloxane molecule has 3 to 100 silicon atoms and pentaerythritol tri(meth)acrylate is employed as the methacrylate ester, the pentaerythritol ester being used in an amount of 0.05 molar to equimolar amounts relative to the COH- and SiX-groups. PA1 a has a value of 1.8 to 2.2, and PA1 b has a value of 0.004 to 0.5; PA1 X is a hydrolyzable radical or a hydroxyl radical, PA1 a has a value of 1.0 to 2.2, and PA1 b has a value of 0.001 to 1.6, is reacted with hydroxyl group containing acrylate or methacrylate esters, preferably in equimolar amounts based on the COH and SiX groups, and wherein either
After the addition of known initiators, these compounds can be cured in a very short time by UV radiation. The curing time generally is less than one second. These compounds can therefore be used, for example, as a vehicle or a vehicle additive for printing inks. Such printing inks can be fixed on the support by UV radiation and exhibit hydrophobic properties, which is of special importance for printing inks whose hydrophobicity is to be utilized technically.
The compounds can, however, also be used for the preparation of lacquer vehicles or other coating materials, such as, for example, as basic materials or additives for coating paper, wood or metal surfaces. Here also, the curing time, which is frequently reduced to fractions of a second, is of special technological importance.
German Pat. No. 27 47 233 discloses that other curable unsaturated compounds, which are capable of copolymerizing, may be added to these compounds in order to influence the properties and/or to lower the costs of the systems.
German Offenlegungsschrift No. 29 48 708 discloses a process for synthesizing organopolysiloxanes which are suitable for use as active ingredients in abhesive coating compositions for two-dimensional carriers, and especially, for paper or plastic films. The synthesis is carried out by reacting organopolysiloxanes which have SiCl groups with pentaerythritol triacrylate or pentaerythritol trimethacrylate, optionally with the addition of neutralizing agents that bind hydrogen chloride.
This process has the following principal characteristics:
(a) the organpolysiloxane used has the formula ##STR2## in which R.sup.1 is an alkyl group with 1 to 4 carbon atoms, a vinyl and/or a phenyl group, with the proviso that at least 90 mole percent of the R.sup.1 groups are methyl groups,
(b) the reaction is carried out with at least equimolar amounts of pentaerythritol triacrylate or pentaerythritol trimethacrylate; and
(c) the product of the process is separated by known procedures from solid components suspended in it.
This process may be modified by initially reacting the organochlorosilanes with, based on the SiCl groups, at least twice the molar amount of a dialkylamine, the alkyl groups of which, in each case, have 3 to 5 carbon atoms, the carbon atom adjacent the nitrogen carrying at most one hydrogen atom. The reaction product is then allowed to react with pentaerythritol triacrylate or pentaerythritol trimethacrylate.
These compounds can also be used as coating compositions and cured by UV radiation in the presence of radical initiators. The compounds possess abhesive properties after curing.
In practice, however, it has turned out that these known acrylate or methacrylate modified organopolysiloxanes do not fulfill all the requirements needed for their practical application. In particular, it is desirable to increase the adhesion of the resins to the substrate and, at the same time, to improve the abhesive surface properties. After being fully cured, these compounds should be particularly abhesive towards adhesives so that the resins are suitable especially for coating papers, to which, for example, labels are detachably adhered.